Re: "Proper Gamut Mapping"
Re: "Proper Gamut Mapping"
- Subject: Re: "Proper Gamut Mapping"
- From: Todd Shirley <email@hidden>
- Date: Fri, 14 Dec 2007 12:44:30 -0500
Hi Graeme
I'm interested in this thread, but I'm getting confused, so hopefully
you can clarify. It seems like you didn't respond to Marco's question
because he used the word "convert" instead of "mapped". In your post
(below) you say "mapped from an unspecified non-specific source gamut
to a specific destination gamut" which to me implies a conversion, and
if it doesn't, what do you mean? Are you referring to the fact that a
conversion using standard ICC profiles requires 2 profiles because
each profile can only describe one device, and therefore the
destination profile is converting from a "non-specific source gamut"
because it, by itself, does not "know" the source? How is this a
problem, considering you must use a source and destination profile for
any conversion?
My (limited) understanding of device-links is that they more-or-less
just roll two device profiles into one, thus fulfilling your
requirement that proper gamut mapping is "mapped from a specific
source gamut to a specific destination gamut". How is this gamut
mapping better than using two discrete profiles?
I get confused when you say "how can the source profile have any
affect on the gamut mapping ?" Perhaps I don't understand exactly how
all this works, but doesn't the source profile convert the color
information into LAB using the source gamut, thus resulting in a set
of LAB numbers that are limited to the source gamut? Then when this
information is passed to the destination profile, isn't the source
gamut implied because all the LAB numbers fall within the source
gamut? So it seems to me that even though the "gamut mapping has
already been hard coded into the destination profiles B2A table",
because the LAB numbers are limited to the source gamut the
destination gamut is "informed" by the source gamut? When I write it
out like this, I see that maybe there could be a problem with this
transform, but I can't quite get my head around it. Clearly you have a
better idea, so I'd appreciate if you could clarify why a device
profile transform is better!
Thanks for your time.
–––
Todd Shirley
Urban Studio
New York, NY
On Dec 13, 2007, at 8:21 AM, Graeme Gill wrote:
Marco Ugolini wrote:
How does one convert from an "unspecified, non-specific source
gamut"?
Sorry, you're asking the wrong person, since I've never attempted such
a thing. You should instead direct this question at all the other
vendors of profile creation software :-)
In Photoshop, even if the file is untagged, the working space
becomes the
source profile. So, there is always a specific source profile in the
conversion.
Right, but since the gamut mapping has already been hard coded into
the destination profiles B2A table, how can the source profile have
any affect on the gamut mapping ?
Graeme Gill.
_______________________________________________
On Dec 13, 2007, at 12:19 AM, Graeme Gill wrote:
MATT LARMOUR wrote:
Would you care to elaborate on what you mean by "proper gamut
mapping"?
As in: gamut mapped from a specific source gamut to a specific
destination gamut. As opposed to: mapped from an unspecified,
non-specific source gamut to a specific destination gamut,
the latter being the case with most ICC device profiles people
create.
Graeme Gill.
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